So is the grindind noise only when you're completely stopped (and any movement makes it go away)? Or does it grind at low speeds, but not at higher speeds?
You might try stopping on a downhill slope, shifting to Neutral, and letting 'er roll. You could even turn the engine off (at a stop) and let 'er roll down the hill. That will help you to see if it's coming from the brakes / wheels or the drivetrain.